In the electrical connector art, insulation material often must be removed from a longitudinal extent of an electrical conductor such as an insulated electrical conductor prior to assembly of electrical connectors to stripped and exposed conductor or wire lengths. One well known and widely used method for mechanically stripping insulation material is with a pair of opposed bypassing stripping blades for stripping insulation from an electrical conductor such as a wire, such wire stripping performed in automated lead making apparatus, bench-mounted or hand-held apparatus. According to this method, the opposed pair of stripping blades exerts a wedging-type displacement action along the length of the wire to strip a selected annular length of insulation material from the wire. Thus, an increased depth in the cut, due to for example a thicker insulation or a less acute angular cut, results in a greater "wedging" effect in the insulation, thereby requiring displacement of a greater amount of the insulation material. This "wedging" action thus impedes penetration of the blade and hampers achievement of a uniform cut of the insulation material. Moreover, when a cut is made near the end of the conductor, the blade on one side of the wire tip may more easily and disproportionately displace the insulation material since there is no counter force applied against that conductor end to resist insulation movement.
Thus, several important problems exist in the related art affecting uniform stripping of insulation material when the stripping blades do not uniformly penetrate to substantially the same insulation depth with respect to the conductor. First, if one blade is so deep as to almost contact the electrical conductor while the second opposing blade extends to a more shallow depth, further cooperating blade closure cannot be effected without risking damage to the conductor, thereby resulting in an uneven, non-uniform stripping action. See, for example, Prior Art FIG. 1 showing a pair of opposed uniformly-shaped and finished stripping blades 10 inserted to significantly non-uniform depths through opposing walls of the insulation material 11. The sharp cutting edges 12 of the blade tips are intended to cut and then strip away a portion (insulation slug) of the insulation material 11 encasing the center conductor 13 as the conductor is moved in the direction indicated by arrow A. A further view of a single one of the stripping blades 10 is shown in FIGS. 2-4, whereby the stripping blade 10 includes two inwardly acute angled cutting surfaces 16 converging at a vertex 14 positioned on a longitudinal axis 15. The cutting edges 12 extend along the acute angled cutting surfaces 16 from the longitudinal axis 15 to intermediate extents inwardly of transverse edges 17 of the stripping blade 10. With particular reference to FIGS. 3 and 4, the stripping blade 10 includes an angular flat 18 (having a lateral thickness indicated by arrow B), at the leading outboard edges of the blade 10, and a square flat 20 (having a lateral thickness indicated by arrow C) extending the full length of both cutting edges 12. As previously described, opposing stripping blades 10 having the same cutting parameters typically result in a non-uniform cut of the insulation material. One of each exemplary blade edge is shown in FIG. 5, including a sharp edge 26 of stripping blade 28 shown in FIG. 5(b), a stropped edge 30 of stripping blade 32 shown in FIG. 5(c), and a flat edge 34 of stripping blade 36 shown in FIG. 5(d). It will be understood that matching pairs of such stripping blades 28, 32, 36 are known for use according to the related art. Thus, irrespective of the type of stripping blade and edge selected when used in matched pairs, when blade closure is uneven, some of the insulation on the more shallow cut side will be torn away rather than cut away as would occur with the opposing deeper cutting stripping blade 28, 32, 36. This tearing effect increases insulation slug pull-off force, and also results in a ragged insulation end, which more likely will vary from the desired theoretical, cut plane. Excess strip length variation also increases the chance of untrimmed insulation remaining in the portion of wire to be crimped in a terminal to be applied to the conductor or wire end. In those instances where the insulation wall is very thin, uneven penetration of the stripping blades prevents solid engagement by one blade, thereby hindering slidable removal of the partially severed insulation annulus comprising the insulation slug. A further problem identified in the prior art is insulation compression that results in slippage between the stripping blades and also prevents complete stripping. Furthermore, uneven penetration by the opposing stripping blades will cause the conductor or wire to be deflected from the intended wire path during cutting, thus causing loss of a cut/tear plane having an orientation normal to the conductor, and also detrimentally resulting in a portion of the insulation material being captured by a crimp portion of a connector to be joined to the wire.
According to the related art, it is known that cutting and stripping operations easily break the extremely thin edge of a perfectly sharp blade, as shown in FIG. 5(a). However, depending on grain structure of the base metal and loading conditions on the blade, the breaking tip material may rip adjacent material from the blade. This ripping or chipping is more likely to occur when the blade tip is loaded in bending as is typical of the case when a cooperating pair of stripping blades pull an insulation slug off of a conductor end. Further blade edge deterioration in this uncontrolled fashion results in an uneven and unpredictable cutting profile and the service life of the blade is rapidly diminished. It is known, however, that if this sharp and fragile blade edge is slightly dulled in a usable configuration, its service life may be significantly enhanced. One method of creating this slightly dull edge is by stropping, either manually or by machine so that the finished cutting edge has a very small flat or radius at the tip of the cutting edge instead of a converging sharpened edge, as shown in FIGS. 5b and 5c. If the flat or radius is small enough, on the order of a few thousandths of an inch, the blade will still cut adequately in many applications. Notwithstanding this improvement, however, if the same dulling feature is applied to the edges of opposing stripping blades to provide the same cutting features on both blades, the prior art problem of non-uniform stripping described above still remains.
Accordingly, there remains a need in the art for an apparatus and method of providing stripping blades, which when paired for cooperating bypass stripping action, achieves uniform stripping of insulation material from electrical conductors and overcomes the related art problem of non-uniform stripping. Specifically, it is desired to provide cooperating stripping blades and a method of use thereof to substantially equalize the depth and quality of cut by the stripping blades to achieve uniform and consistent stripping of insulation material from an insulated conductor.